1. Field of the Invention
The present invention generally relates to rotary vane pumping machines, and more particularly, to a rotary positive-displacement scavenging device that communicates with the vane cells of the pumping machine to provide versatility in isolating, scavenging, and/or accessing the respective contents of the vane cells to enhance the performance of the rotary vane pumping machine.
2. Description of the Related Art
The overall invention relates to a large class of devices comprising all rotary vane (or sliding vane) pumps, compressors, engines, vacuum-pumps, blowers, and internal combustion engines. Herein the term pumping machine refers to a member of a set of devices including pumps, compressors, engines, vacuum-pumps, blowers, and internal combustion engines. Thus, this invention relates to a class of rotary vane pumping machines.
This class of rotary vane pumping machines includes designs having a rotor with slots with a radial component of alignment with respect to the rotor's axis of rotation, vanes which reciprocate within these slots, and a chamber contour within which the vane tips trace their path as they rotate and reciprocate within their rotor slots.
In alternate embodiments, the vanes may slide with an axial component of vane motion, or with a vector that includes both axial and radial components. The vanes may also be oriented at any angle in or orthogonal to the plane illustrated, whereby the vanes would also slide with a diagonal motion in addition to any axial or radial components. The vane motion may also have an arcuate component of motion as well. In all cases, the reciprocating vanes extend and retract synchronously with the relative rotation of the rotor and the shape of the chamber surface in such a way as to create cascading cells of compression and/or expansion, thereby providing the essential components of a pumping machine.
Some means of radially guiding the vanes is provided to ensure near-contact, or close proximity, between the vane tips and chamber surface as the rotor and vanes rotate with respect to the chamber surface. Certain radial guidance designs were described in pending U.S. patent application Ser. Nos. 08/887,304, to Mallen, filed Jul. 2, 1997, entitled "Rotary-Linear Vane Guidance in a Rotary Vane Pumping Machine" ('304 application); and 09/187,705, to Mallen, filed Nov. 4, 1998, entitled "Rotary-Linear Vane Guidance in a Rotary Vane Pumping Machine" ('705 application). The '304 and '705 applications describe a vane guidance means that overcomes a common shortcoming of the conventional means of guiding the vanes, namely that high linear speeds are encountered at the radial-guidance frictional interface. These high speeds severely limit the maximum speed of operation and thus the maximum flow per given engine size.
In the improved sliding-vane pumping geometry of the '304 and '705 applications, multiple vanes sweep in relative motion against the chamber surfaces, which incorporates a radial-guidance frictional interface operating at a reduced speed compared with the tangential speed of the vanes at the radial location of the interface. The linear translation ring interface permits higher loads at high rotor rotational speeds to be sustained by the bearing surfaces than with conventional designs. Accordingly, much higher flow rates are achieved within a given size pumping device or internal combustion engine, thereby improving the performance and usefulness of these machines.
However, even with the above advantages, efforts continue in order to further refine and enhance the performance of the rotary machine. In particular, for an internal combustion engine application, a two-stroke design achieves very high flow rates and power density yet is limited in the range over which the load may be "throttled" because of the impracticality of a vacuum-throttle system. Because the two-stroke cycle does not provide positive-displacement purging of exhaust gases and positive-displacement suction and induction of an intake charge, a conventional vacuum-throttle system cannot be effectively employed without adding external pumping devices. Although a positive-displacement ancillary pump may be added to a two-stroke vane engine for scavenging and vacuum-throttle, such a system imposes additional penalties of complexity, friction, thermal constraints, weight, size, performance limitations, and/or cost.
Whereas the pumping hardware and mechanism for the primary engine cycle (compression, combustion, and expansion) is designed to contain pressures on the order of 2000 psi, the scavenging mechanism need only handle pressures on the order of 20 psi. In addition to this two order of magnitude reduction in pressures, the scavenging mechanism need not address the many complex constraints imposed on the internal combustion pumping mechanism, such as crevice volumes, dramatic heat flux rates and associated expansion issues, surface area-to-volume ratios, critical sealing performance, and many other factors. For these reasons, it would be inefficient to employ the primary pumping mechanism for the purpose of scavenging the gases and providing a vacuum throttle. This inefficiency would manifest itself in a dramatic reduction in power density and a dramatic increase in cost, by moving to a four-stroke design to achieve scavenging and vacuum throttle. In short, the primary pumping mechanism of an internal combustion engine is an overly bulky and slow means to employ for the task of positive-displacement scavenging.
Therefore, there exists a need for a simple high-speed rotary mechanism, which, when mated to and meshed with a vane pumping machine, will provide rapid positive-displacement scavenging and vacuum throttle capability to the vane cells without imposing a significant penalty in power density, cost, or complexity.